Pond Size Calculator
Enter the length, width and average depth of your pond in metres and choose its shape. You get the water volume, the liner size to order, the pump flow and a safe fish number.
- Volume in litres
- Liner and underlay
- Pump flow by fish type
Use average depth for volume. For liner size, the calculator uses the same figure, so enter the maximum depth if your pond has shelves.
Volume decides almost everything in a pond. The pump, the filter, the treatment doses and the number of fish all scale with how much water you have. Liner size is different. It depends on the length and width plus twice the deepest depth, because the liner has to run down one side and back up the other.
Pond sizes and liners
Common garden pond sizes. Search for a size or volume.
| Pond (m) | Depth (m) | Volume (L) | Liner (m) | Pump (L/h, goldfish) |
|---|---|---|---|---|
| 1.5 × 1.0 | 0.5 | 750 | 3.1 × 2.6 | 375 |
| 2.0 × 1.5 | 0.6 | 1800 | 3.8 × 3.3 | 900 |
| 3.0 × 2.0 | 0.8 | 4800 | 5.2 × 4.2 | 2400 |
| 3.0 × 2.5 | 0.9 | 6750 | 5.4 × 4.9 | 3375 |
| 4.0 × 3.0 | 1 | 12000 | 6.6 × 5.6 | 6000 |
| 5.0 × 3.0 | 1.2 | 18000 | 8.0 × 6.0 | 9000 |
| 6.0 × 4.0 | 1.5 | 36000 | 9.6 × 7.6 | 18000 |
Liner sizes include 30 cm of overlap on every edge so you can bury it under slabs or edging. Always order the underlay at the same size as the liner.
How depth changes a pond
A 3 × 2 metre pond at different depths. Slide the average depth to see volume, liner and pump.
Deeper water stays cooler in summer and does not freeze solid in winter. Goldfish do well from 60 cm, and koi need at least 1.2 m.
How to measure a pond
Work in metres for the easiest maths. Step through it.
Mark the outline
Lay a hose or rope on the ground to see the shape.
For an existing pond, a water meter on the hose gives the most exact volume. Note the reading before and after filling.
Wildlife, goldfish or koi
Each pond type has different needs. Pick a type to compare.
Shallow sloping edges for frogs, birds and insects. Plants keep the water clear.
A mix of plants and a modest filter. Fish need deeper water to shelter in.
Large, deep and heavily filtered. A bottom drain and UV clarifier are common.
Koi grow to 60 cm or more and produce a lot of waste. They need large deep ponds and strong filtration. Wildlife ponds are the opposite and work best with shallow edges and no pump.
Before you dig
A pond is hard to move once it is in. Tick each point.
Tick each item as you go.
Call your utility company or use a cable avoidance tool before digging. Power and gas lines are often shallower than people expect.
What you get from the result
Plan the whole pond from one set of numbers. Each tile explains one result.
Litres and US gallons of water.
Length and width including overlap.
Protects the liner from stones.
Litres per hour for your fish type.
A cautious number for adult fish.
Use the volume to dose treatments and size the filter. Filters are usually rated for a pond volume with or without fish, so pick the fish rating.
Frequently Asked Questions
No question matches that search.
How do I calculate pond volume?
Multiply length × width × average depth in metres, then by 1,000 for litres. For an oval pond, multiply by 0.785 as well.
What size liner do I need for my pond?
Length plus twice the maximum depth plus 60 cm, by width plus twice the maximum depth plus 60 cm.
How big a pump do I need?
Enough to move the full volume every 1 to 3 hours, depending on fish. A 4,800 L goldfish pond needs about 2,400 L/h.
How deep should a fish pond be?
At least 60 cm for goldfish and 1.2 m for koi. Deeper water stays a steadier temperature.
How many fish can I keep in my pond?
About one goldfish per 200 litres and one koi per 1,000 litres, measured at adult size.
How do I measure an irregular pond?
Use the longest length and widest width and choose irregular. The calculator scales by 0.85 to allow for curves.
Does a wildlife pond need a pump?
No. Plants keep the water healthy. A small solar fountain can help if mosquitoes are a problem.
Build a pond that stays healthy
Measure carefully, use the average depth for volume and the maximum depth for the liner, then size the pump and filter to the fish you plan to keep. A pond built around its real volume is far easier to keep clear.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.